Enhancement of aerobic granulation by zero-valent iron in sequencing batch airlift reactor

This study elucidates the enhancement of aerobic granulation by zero-valent iron (ZVI). A reactor augmented with ZVI had a start-up time of aerobic granulation (43 days) that was notably less than that for a reactor without augmentation (64 days). The former reactor also had better removal efficiencies for chemical oxygen demand and ammonium. Moreover, the mature granules augmented with ZVI had better physical characteristics and produced more extracellular polymeric substances (especially of protein). Three-dimensional-excitation emission matrix fluorescence showed that ZVI enhanced organic material diversity. Additionally, ZVI enhanced the diversity of the microbial community. Fe(2+) dissolution from ZVI helped reduce the start-up time of aerobic granulation and increased the extracellular polymeric substance content. Conclusively, the use of ZVI effectively enhanced aerobic granulation.

Investigation on the behavior of austenite and ferrite phases at stagnation region in the turning of duplex stainless steel alloys

This paper investigates the deformation mechanisms and plastic behavior of austenite and ferrite phases in duplex stainless steel alloys 2205 and 2507 under chip formation from a machine turning operation. SEM images and EBSD phase mapping of frozen chip root samples detected a build-up of ferrite bands in the stagnation region, and between 65 and 85 pct, more ferrite was identified in the stagnation region compared to austenite. SEM images detected micro-cracks developing in the ferrite phase, indicating ferritic build-up in the stagnation region as a potential triggering mechanism to the formation of built-up edge, as transgranular micro-cracks found in the stagnation region are similar to micro-cracks initiating built-up edge formation. Higher plasticity of austenite due to softening under high strain is seen responsible for the ferrite build-up. Flow lines indicate that austenite is plastically deforming at a greater rate into the chip, while ferrite shows to partition most of the strain during deformation. The loss of annealing twins and activation of multiple slip planes triggered at high strain may explain the highly plastic behavior shown by austenite.

Acetylation of alcohols and phenols using continuous-flow, tungstosilicic acid-supported, monolith microreactors with scale-up capability

A highly scalable and efficient flow-system has been developed to perform the catalyzed acetylation of alcohols and phenols, such as salicylic acid, at room temperature in excellent yield. The volumetric throughput and the amount of product can be increased simply by increasing the diameter of a versatile catalytic 12-tungstosilicic acid-supported, silica monolith can be used to increase the quantity of product produced without having to changeing the optimal operatingreaction conditions.

Influence of deformation conditions and texture on the high temperature flow stress of magnesium AZ31

The evolution of hot working flow stress with strain is examined in torsion, uniaxial compression and channel die compression. The flow stress was found to be strongly dependent on texture and deformation mode. At low strains this dependency accounted for a difference in flow stress of up to a factor of two. At higher strains the influence of texture and deformation mode was less marked. The stresses corresponding to an equivalent strain of 0.5 were modelled using a power law expression with an activation energy of 147 kJ/mol and a strain rate exponent of 0.15. The influence of texture and deformation mode on flow stress is rationalised in terms of the influence of prismatic slip, twinning and dynamic recrystallisation on deformation stress and structure.

How world's best public relations practice was not, but might have been achieved, in respect of a "biosolids" (stabilised sewage sludge) project

This is a case study which criticises the way a water authority has been trying to introduce “biosolids” (stabilised sewage sludge) projects. Two proposed projects have been abandoned after outcry by communities neighbouring earmarked sites. At the time of writing a third project was going ahead. This local scale clash reflects contests which are cropping up globally as water authorities are restricted in their use of land or sea dumping and ordered to introduce environmentally sustainable practices. The case study ends with a discussion of a strand of cultural theory which might have given the water authority a better understanding of the public issues involved. The article concludes that understanding cultural theory might assist organisations achieve world best practice in public relations when they face some of the pressing environmental and safety concerns of the 21st century.

A sensitive procedure for the rapid determination of arsenic(III) by flow injection analysis and chemiluminescence detection

A novel chemiluminescence flow injection procedure for the determination of As(III) in aqueous samples is described. The method involves injection of As(III) samples into a 1% (m/v) sodium hexametaphosphate in 0.02 M H₂SO₄ carrier stream, which then merges at a Y-piece with a reagent stream consisting of potassium permanganate (5.0 × 10⁻⁵ M) made up in the acidic sodium hexametaphosphate carrier solution. The chemiluminescence intensity of the resulting reaction mixture was measured at a photomultiplier tube operated at a voltage of 0.93 kV. Under optimized conditions, the method is characterised by a linear range from 0.5 to 5.0 μg l⁻¹, a detection limit of 0.3 μg l⁻¹ and a sampling frequency of 150 h⁻¹. The effects of common anionic and cationic interferences were investigated, and it was found that the only ions to cause serious interference were those which react with potassium permanganate, namely sulphide, iodide and ferrous.

Stability of oxide films formed on mild steel in turbulent flow conditions of alkaline solutions at elevated temperatures

In the industries involving alkaline solutions in different process streams, the nature and stability of oxide films formed on the metallic surfaces determine the rates of erosion–corrosion of the equipment. In the present study the characteristics of the oxide films formed on AISI 1020 steel in a 2.75 M sodium hydroxide solution at temperatures up to 175°C, have been investigated by employing electrochemical techniques of cyclic voltammetry and chronoamperometry. The experiments were carried out in an autoclave system based upon a ‘rotating cylinder electrode’ geometry to determine the effects of turbulence on the stability of the films. The results suggest that little protection is afforded in the active region (at about −0.8 V_SHE). In the passive region at low potentials (−0.6 V to −0.4 V_SHE), it appears the films are compact and more stable, and therefore provide good protection. At higher potentials (>−0.4 V_SHE) in the passive region, the results suggest that film formation and dissolution occur simultaneously and the increase in temperature and turbulence causes a breakdown of the passive film resulting in a situation similar to nonprotective magnetite growth.

Correlation between shoulder flow zone quality and material flow quantity during friction stir welding of thick aluminum section using scroll shoulder tool

The so-called scroll shoulder tool is widely used particularly for thick section friction stir welding (FSW). However, the correlation between its shoulder flow zone weld quality and material flow quantity remains unclear. This information is important for tool design. In the present study, a scroll shoulder tool was used to FSW 20mm thick 6061 aluminum (Al) plates at a range of welding parameters. The pick-up material (PUM) by the scroll was quantified, and the effect of welding parameters and PUM on the shoulder flow zone formation and weld quality was studied. It was found that there is a positive linear relationship between the PUM and weld quality. In order to obtain a defect-free FSW weld produced by the scroll shoulder tool, scroll groove needs to be fully filled by PUM.

Material flow forming the shoulder flow zone using scroll shoulder tool during friction stir welding of thick section aluminum alloys

Scroll shoulder tools are widely used and they do not need to be tilted during friction stir welding (FSW). However, the detailed material flow, which is important for proper scroll shoulder tool design and subsequently for forming the defect-free shoulder flow zone, has not been fully explained. In the present study, features of material flow in shoulder flow zone, during FSW of thick 6061 aluminium (Al) plates using a scroll shoulder tool were investigated. It was observed that there is a simple layer-to-layer banded structure which appears in the bottom portion of shoulder flow zone, but disappears in the top portion of this weld zone. When the scroll shoulder tool is plunged into the workpiece to a determined depth, the workpiece material is extruded by the tool pin, and pushed up into the scroll groove beneath the shoulder forming the pick-up material. During the forward movement of the tool, the central portion of pick-up material was driven downward by the root portion of pin and then it detaches from the tip portion of pin in a layer-to-layer manner to form the weld.

Performance of an oxidation ditch retrofitted with a membrane bioreactor during the start-up

The objective of this study is to elucidate the full-scale characteristics of an oxidation ditch (OD) retrofitted with a membrane bioreactor (MBR). Domestic wastewater entering an oxidation ditch at a flow rate of 86 m3/d was directed to a MBR retrofitted into the original secondary sedimentation tank. The MBR contained flat sheet membranes. The data collected for 2 months during the start-up of the system showed that pH was maintained at 7.2 and 6.7 in OD and MBR, respectively. Dissolved oxygen (DO) in MBR remained stable at 7.8 mg/L, while fluctuated in OD. The mixed liquor suspended solids (MLSS) in the OD remained steady at a concentration about 1000 mg/L, but it was gradually building up from 500 mg/L to 2400 mg/L in the MBR during this period. Measurements of carbohydrate and protein were made by extracting the extra cellular polymeric substances (EPS) with sodium hydroxide (NaOH) from the mixed liquor obtained from both OD and MBR. Carbohydrate was predominant in the EPS and the ratios between carbohydrate and protein converged to fixed values from the fourth week; in this case the ratio was 4.5 for OD and 5 for MBR. The variation in EPS contents showed similar trends in both OD and MBR. The integrated treatment facility removed ammonia, COD and BOD at 100, 91.6 and 97.0%, respectively. However, efficiency of nitrate and phosphate removal has not been realized yet.

The in situ physiology of "Nostocoida limicola" II, a filamentous bacterial morphotype in bulking activated sludge, using fluorescence in situ hybridization and microautoradiography

The in situ physiology of the actinobacterial bulking and foaming filamentous bacterium "Nostocoida limicola" II was studied by fluorescence in situ hybridization/microautoradiography. Substrate assimilation patterns of pure cultures of this bacterium were different to those seen in activated sludge biomass samples. There was no evidence to suggest that "N. limicola" II preferred hydrophobic substrates, but evidence was produced to support the view that it is metabolically active under anaerobic conditions in activated sludge.

Evaluating the performance of different media in a horizontal subsurface flow constructed wetland

The treatment efficiency of a wetland system requires a balance between pollutant loading rate and hydraulic retention time (HRT), hydraulic loading rate (HLR) and the suitable substrate to be used. The aim of this study was to investigate the treatment efficiency of horizontal subsurface flow constructed wetland planted with phragmites australis and scirpus maritimus containing three different substrates to treat agricultural wastewater under short term operation. Alum sludge and zeolite were used as substrates and gravel was used as a control for a laboratory-scale horizontal flow constructed wetland (CW) units that were made of high-density Polyethylene. The units were operated under 2, 3 and 4 days of HRTs and at different HLR for each substrate. Each beds received 0.012 m3/d to 0.08 m3/d of synthetic wastewater corresponding to a HLR of 0.035 to 0.243 m/d and a COD loading rate of 0.0148 kg COD (m2.d)-1 to 0.026 kg COD (m2.d)-1. The relationships between the substrate, retention time and removal efficiency, especially of organic matter and nutrient removal were investigated. All units showed relatively stable removal for COD during the entire operational period. The COD removal for all units and HRT were in ranged from 67% to 93%. The zeolite unit achieved significantly higher removal of TN, NH4-N and TSS compared to alum sludge and gravel unit at all HRT. The unit with zeolite was highly effective in removing TN (54 to 96%), NH4-N (50 to 99%) and TSS (91 to 96%) respectively, at 2, 3 and 4 days of HRT. Meanwhile, alum sludge was highly effective in removing phosphate. The removal of phosphate from alum sludge unit was ranged from 94 to 97% for all HRT. Compared to gravel CW unit, zeolite and alum sludge CW were proved to be tolerant to high organic loadings and nutrients, suggesting these substrates as viable options for biological treatment of agricultural wastewater.